Thin film photovoltaic (PV) modules (also referred to as “solar panels”) based on cadmium telluride (CdTe) paired with cadmium sulfide (CdS) as the photo-reactive components are gaining wide acceptance and interest in the industry. CdTe is a semiconductor material having characteristics particularly suited for conversion of solar energy to electricity. For example, CdTe has an energy bandgap of about 1.45 eV, which enables it to convert more energy from the solar spectrum as compared to lower bandgap semiconductor materials historically used in solar cell applications (e.g., about 1.1 eV for silicon). Also, CdTe converts radiation energy in lower or diffuse light conditions better compared to the lower bandgap materials and, thus, has a longer effective conversion time over the course of a day or in cloudy conditions as compared to other conventional materials.
The junction of the n-type layer and the p-type layer is generally responsible for the generation of electric potential and electric current when the CdTe PV module is exposed to light energy, such as sunlight. Specifically, the cadmium telluride (CdTe) layer and the cadmium sulfide (CdS) form a p-n heterojunction, where the CdTe layer acts as a p-type layer (i.e., an electron accepting layer) and the CdS layer acts as an n-type layer (i.e., an electron donating layer). Free carrier pairs are created by light energy and then separated by the p-n heterojunction to produce an electrical current.
It is generally desired to include at least one dopant (e.g., copper) in the cadmium telluride layer in the final device. For example, copper can be added to the cadmium telluride layer by treating the layer with copper chloride and heating. However, this treatment step adds significant processing requirements to the manufacture of the PV device, since it involves the use of copper chloride, which is a toxic chemical material.
As such, a need exists for methods of doping the absorber layer (e.g., a cadmium telluride layer) while limiting the processing steps required in the manufacturing process and/or avoiding the use of toxic treatments (e.g., copper chloride).